Field of the Invention
The present invention relates to fuel-resistant liquid asphalt binder. Specifically, embodiments of the present invention relate to a fuel-resistant liquid asphalt binder for improving one or more properties of a bituminous asphalt mix including, but not limited to, workability, flowability, corrosion resistance in the presence of a fuel, and resistance to fatigue cracking.
Background Art
Aside from roads and parking lots, one of the largest uses of pavement is for airport runways and tarmacs. Typically, the pavement is either concrete or a Hot Mix Asphalt (HMA). Concrete pavement is typically comprised of various Portland concrete cements mixed with aggregates and water. Concrete pavement is poured in place at an ambient temperature and it hardens as the concrete dries.
A HMA, on the other hand, is typically made using a liquid asphalt binder, which is a liquid residue left over after the lighter petroleum distillates have been removed from petroleum crude oil during a refining process. The binder is mixed with an aggregate and hauled to the place where it is to be installed. The paving process of HMA involves either laying a bed of asphalt mixture onto a prepared road bed or applying a thin overlay over an existing layer of pavement. The HMA is then compacted under controlled conditions using a roller or compactor while the mixture is still hot in order to achieve a predetermined density or air void content.
When HMA is used in airports, jet fuel is continually spilled onto the tarmac of the runways and taxiways while aircrafts are parked, taxiing, or awaiting clearance. This spillage can occur either through thermal expansion of fuel from the overflow port of the storage tank of an aircraft or a refueling vehicle, or from fuel being spilled during refueling. Upon contact with the HMA surface, the fuel will degrade the HMA and the HMA will eventually deteriorate and fall apart. Over time, this causes the pavement to rut and crack under the weight of an aircraft and other equipment. This reduces the effective life of these surfaces, resulting in premature replacement and repair, which increases the life-cycle costs of the runways and taxiways.
Historically, this problem has been solved in one of two ways. The first solution has been to replace the HMA pavement with a concrete surface, especially in areas that are prone to continual fuel spills. However, this solution has the drawback of being more expensive than using HMA and requires much longer down time to complete the job, which can be detrimental in busy airports.
The second solution has been to seal the surface of the HMA pavement by using a coal tar sealer applied to the surface. However, the use of coal tar sealers has three major drawbacks. First, coal tar has a coefficient of expansion different from a petroleum-based asphalt pavement. This can cause severe cracking of the sealer and breaches in the fuel-resistant layer. These cracks can allow fuel spills to penetrate into the pavement, causing further deterioration of the HMA underneath. Therefore, reapplication of the coal tar sealer every two or three years becomes necessary to maintain fuel resistance. Second, coal tar sealers are categorized as carcinogenic materials. Application of the coal tar sealers on HMA pavements introduces carcinogenic material into the pavement material, which is often recycled and used again in repaving operations. If not handled properly, workers may be exposed to coal tar fumes. Third, the coating must adhere to the surface of the HMA and there is the possibility that water and other foreign materials will leak through cracks in the coating into the junction between the coating and the surface. These foreign materials can compromise the ability of the coating to bind with the surface, which can be made worse by freezing and/or mechanical action at the junction. This problem is further exacerbated in airports by the weight of large aircraft on the surface.
One of the more recent developments in the HMA industry has been the development of polymer-modified asphalt binders. Polymer-modified asphalt binders can be used to make HMA with increased resistance to permanent deformation, reflective fatigue, and thermal cracking Unfortunately, spillage of jet fuel that softens standard HMAs will also soften the commonly used polymer-modified asphalts, resulting in a decrease of the integrity (stability) of the asphalt. Thus, while enjoying some benefits over the traditional HMA formulations, the polymer-modified asphalts still require an application of coal tar sealants in order to resist fuel spills.
Efforts have been made to increase the fuel resistance by using coating for HMA. U.S. Pat. No. 5,010,129 provides an example of such a fuel-resistant coating. However, coatings are problematic because the adherence of the coating to the HMA surface will deteriorate over time, which can result in cracking. These cracks can allow fuel spills to penetrate into the pavement, causing further deterioration of the HMA underneath
As such, there is a need for an HMA that resists deterioration from exposure to corrosive substances, such as fuel and hydraulic fluid, in particular jet fuel, and that has longer longevity than either a standard HMA pavement or an asphalt pavement having a fuel-resistant coating. The HMA should resist deterioration without requiring the application of coal tar and withstand the high standing weight of aircraft and commercial vehicles without rutting and failure.